RFR: CODETOOLS-7903400: DEFAULT_UNIX_ENV_VARS needs to be updated [v3]

[Jonathan Gibbons]

> Please review a small change to add additional environment variables that may be required on some Unix-like platforms.
> 
> The additions include:
> * `DBUS_SESSION_BUS_ADDRESS`
> * `WAYLAND_DISPLAY`
> * all `XDG_*` variables
> 
> There is some related additional cleanup in this area as well.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  Fix GDMSESSION

-------------

Changes:
  - all: https://git.openjdk.org/jtreg/pull/152/files
  - new: https://git.openjdk.org/jtreg/pull/152/files/45f761b0..9b7384d9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=152&range=02
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=152&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/152.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/152/head:pull/152

PR: https://git.openjdk.org/jtreg/pull/152